At the moment when the Soviets conducted his first nuclear test, the RDS-1 in 1949, they could see on field the flaws of the first weapon designs. The RDS-1 was build under a ultimatum have gone by Joseph Stalin after the American nuclear bombing over Japan, in which he ordered developed a nuclear bomb within 5 years. Consequently they did not planned a posterior nuclear program, but they had some designs (RDS-2, RDS-3, RDS-4 and RDS-5). Leading the project was Lavrenti Beria, who ordered that the bomb was a exact copy of the Fat Man, although the soviet scientists had gone much improvements in designs. Beria did not wanted apply this discoveries to the first soviet bomb because he distrusted the information related to the nuclear weapons, even the information compiled with the spies.

Up until 1947, all four implosion bombs that had been exploded by USA had all been identical, based on a conservative wartime design (a solid plutonium core). The Sandstone test series intoduced a second generation of weapon design by evaluating several new design principles and variation of a number of design parameters to evaluate their effects on performance. The Sandstone devices all replaced the contiguous tamper-core approach with a "levitated core" in which the core was suspended within a larger hollow space within the tamper so that a gap existed between them. The collision between the tamper and core would create more efficient compression of the core. These devices also abandoned the use of a pure plutonium core since oralloy (uranium hihgly enriched in U-235) production exceeded plutonium production by a factor of over 3-to-1. Other tested features included: varying the tamper thickness; varying the amount of fissile material in the core; and the effect of using a "minimum strength" polonium-beryllium Urchin neutron initiator.

With the experience obtained by the Americans, plus the theorist advances that the soviets scientist were obtained, in 1951 the committee of Arzamas-16 (KB-11) started a program of study and build of new nuclear weapon designs, taking the same path that the Americans. The objectives of this program were similar to the "Operation Sandstone", with the exception in the uranio-235 core, which will be studied later. By mid-1951 the Soviets managed to build the two first’s devices of the program: the bombs RDS-2 and RDS-3 (also known as "Mariya" or "Maria"). Their tests were planned to ends of same year. The RDS-2 was a boosted fission bomb with a levitated plutonium core, that including improvements as the reduction of the explosive layer (composite of equal parts of TNT and RDX), and the addition of tritium. The RDS-3 was a device identical to the RDS-2, which differed of it by a levitated composite core, with a plutonium nucleus and a uranium shell.

During the meeting of Council on Science and Technology, where discussed the detonation of this new devices, there was discussion about how conducted the testing. The team of physicists who developed the design and build of the devices, led by Yuli Khariton, suggested that the bombs were detonated on towers, as well as the RDS-1, in order to obtain more accurate data on the performance and development of the chain reaction. Instead, the leaders of nuclear weapons program, led by Igor Kurchatov suggested that the bomb was dropped from the air, to obtain data on its effectiveness as a weapon. Finally, consensus was reached to make an explosion in tower (RDS-2) and one with an air-launched (RDS-3).

The detonation of RDS-2 was programmed to September 24 of 1951, in Semipalatinsk. The test was called Vtoraya Molniya by de Soviets, and was known as Joe-2 in USA. The bomb was assembled in the place of the test shortly before of this for security reasons, and installed in a 30 m tower, around which buildings was built and places several military vehicles to study the effects of the explosion. The bomb exploded with a yield of 38,3 kt. The explosion was seen and heard at 170 km away.
A few days later was realized the first test of the RDS-3 device. Was occurred on October 18, 1951. Like the RDS-2, the bomb was assembled with the nuclear charge shortly before his test, in the same place as this. The bomb was dropped by a Tu-4 aircraft at 10 km height, in Semipalatinsk, exploding on an altitude of 380 m with a yield of 42 kt. The explosion was seen at 170 km away. Given the success of the tests, the designs of both bombs was sent for mass production, making in 1953 the RDS-3 went into service as part of the military arsenal.

After the creation of the bombs RDS-2 and RDS-3, whose designs was quite successfully but only were able to be delivered by heavy bombers, was started the build of tactical nuclear weapons. It was necessary to reduce the size of the bomb and improve the design of the levitated core. The first bomb designed was known as Tatyana, later converted in the RDS-4. Designed by the Arzamas-16 committee, this device was part of a small size tactical nuclear weapons generation, along with the RDS-5. This weapon was a boosted fission bomb with a levitated plutonium core, modified from RDS-2, that used a small explosive amount (composite of TNT and RDX in 50/50) and had a nominal yield of 30 kt. The RDS-5 differed with the RDS-4 only in the core, being the core of the RDS-5 composite of uranium/plutonium.

The first test of a RDS-4 “Tatyana” device occurred on August 23, 1953, in Semipalatinsk. Is known as Joe-5 in USA. An IL-28 aircraft, accompanied by a safety copy and 2 MiG-17, dropped the bomb on an altitude of 11 km, which exploded 600 m from the ground, with a yield of 28 kt. The test was successfully, and the device was sent for mass production. Subsequently developed, based on the RDS-4, design which decreased the amount of plutonium and explosives to make tactical bombs even smaller. Since the RDS-4 was built RDS-4M, identical to this but much smaller size.

Similarly, into the improvements realized in the designs of the first soviet nuclear bombs, at 1950 in Arzamas-16 was started studies about improve of the neutron initiator. In 1952 was achieved to obtain the first design. The new design was implemented in a RDS-3 bomb. This device, called RDS-3I, which was the first soviet nuclear bomb with an external neutron source, was successfully tested on October 23 of 1954 (test called “Joe-12”) in Semipalatinsk. The bomb was airdropped, exploding on an altitude of 410 m and a yield of 62 kt.

Is known that a modified version of the bomb RDS-5 was tested on October 28 of 1954 (in the official Soviet records appears as the October 26) in Semipalatinsk, at the request of Yuli Khariton, to obtain more information about the performance of a new neutron initiator design (the original bomb design was have tested previously). The bomb exploded on an altitude of 110 m with a yield of 2,8 kt. This test was called Joe-13 by the Americans.

The work was directed then to the development of bomb that could be transported by self-propelled missiles. Modified versions of the RDS-4 was used as warhead in medium-range R-5M rocket, and began to design a device that was deliverable by a T-5 torpedo. This new device was called RDS-9. In comparison with others bombs derived of the RDS-4, had to reduce drastically the size of the nuclear core. The works with the RDS-9 was conducted between 1953 and 1954. In the RDS-9 bombs was used a levitated plutonium core, and the proportion 50/50 of the TNT/RDX explosive layer was modified.
On October 19, 1954, in Semipalatinsk, was conducted the first test of the device RDS-9. The bomb was installed into a T-5 torpedo and placed on a 15 m tower. The detonation was a failure. From observation places were seen some low clouds, that were dispersed by the wind, but no indication of any nuclear explosion. Later was measured the radiation in the zone, finding that there was not dispersion of radioactive material. This was the first fizzle in the history of the Soviet nuclear weapons program. In 1955 were conducted 3 successful detonations in Semipalatinsk and one in Novaya Zemlya (Joe-17).

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